<form name="form1" id="form1" method="POST" action="buscar.php">
    <fieldset><legend><span>Buscar Alunos</span></legend>
        <p>
            <label for="coluna">opções:</label>
                <select name="coluna">
                    <option value="nome">nome</option>
                    <option value="cpf">cpf</option>
                    <option value="idade">idade</option>
                </select>
            
              <input type="text" name="valor" id="valor" />
	</p>        
	
        <p>
            <input type="submit" value="Buscar"/>
        </p> 
        
    </fieldset>
</form>
<?php
if ($_SERVER['REQUEST_METHOD']=="POST"){		
	include 'AlunoDAO.php';
        include 'Aluno.php';
        
        $coluna = $_POST['coluna'];
        $valor  = $_POST['valor'];             
	
	$alunoDAO = new AlunoDAO();
	$alunoDAO-> Busca($coluna, $valor);
        
}

?>